Removal of metallic contaminants from hydrocarbon oils with a foaming agent

ABSTRACT

&lt;PICT:0830128/III/1&gt; A process for the removal of surface-active constituents from a hydrocarbon oil comprises foaming a portion of the oil with a gas and separately recovering oil containing surfaceactive compounds and an oil containing a reduced amount of surface-active constituents.  Gases which may be used include carbon dioxide, nitrogen, methane, ethane, propane, propylene, butane, refinery gases, air, ammonia, oxygen and steam.  Condensible gases are particularly suitable since they permit the separated foam to be collapsed by cooling.  Foaming may be assisted by reducing the viscosity of the oil with a diluent, e.g. 200-400 DEG  F. aliphatic fractions, kerosines and heavy naphthas, or by adding water. Whilst most surface-active contaminants occur in fractions boiling above 950 DEG  F. the process is preferably applied to broad cut fractions with an I.B.P. well below 950 DEG  F.  A hydrocarbon oil having a F.B.P. above 950 DEG  F. is introduced into foaming vessel 1 through line 2. A solvent, e.g. between 1 and 4 parts of kerosine, may be added to reduce the viscosity of the oil, either in admixture with the oil in line 2 or separately through line 4. Air or other gas is introduced through line 6 to distributer 7 and the oil level 8 is maintained at a point between the points of introduction of the feed and the gas by removal of product oil through line 9 from a point below distributer 7.  Foam is taken from the top of the column by line 10 to defoaming zone 11 where it is separated into gas which is removed via line 12 and oil enriched in surface-active agents which is either removed via line 14 or recycled to the top of the column via line 15.  Reflux ratios of 1 : 1 to 1 : 10 may be employed.

July 28, 1959 GAS Herman Bleber Inventors Ibrohlm A Eldlb By W di. n U3/LQ, AHorney REMOVAL F lVIlETALLIC CONTAMINANTS FROM HYDRCARBON OILS WITH A FOAM- ING AGENT Herman Bieber, Linden, and Ibrahim A. Eldib, Roselle, NJ., assignors to Esso Research and Engineering Company, a corporation of Delaware Application December 11, 1957, Serial No. 702,040 8 Claims. (Cl. 208-251) The present invention relates to the upgrading of hydrocarbon oils and more particularly relates to a new and improved refining process for removing innate organo-metallic compounds and other surface active materials from hydrocarbon oils.

Organo-metallic compounds are found as innate constituents in most petroleum gas oils and residua boiling in excess of about 950 F. and may be present therein in concentrations as high as 200 pounds per 1000 barrels of oil. Because of the presence of these metallic compounds, such oils are unsuitable for use as high grade fuels, as feed stocks to catalytic cracking units and in other applications of similar nature. In catalytic cracking and hydrofining processes, for example, Imetallic compounds in the feed streams will quickly deactivate the catalysts and cause the production of large amounts of coke and gases. When present in fuels the metals rapidly attack the refractories used to line boilers and combustion chambers; cause slagging and deposit formation upon boiler tubes, combustion chamber walls and gas turbine blades; and severely corrode metallic surfaces with which they come into contact at elevated temperatures. Heretofore no wholly satisfactory method for removing the metals from such oils and thus avoiding these difficulties has been available.

The present invention provides a new and improved method for removing innate organo-metallic compounds and other surface active constituents from hydrocarbon oils and thus opens the way lfor the use of such oils in a variety of applications for which they have been unsuitable heretofore. In accordance with the invention it has now been discovered that organo-metallic constituents of hydrocarbon oils can be readily removed from such oils by introducing gas into the oils under conditions such that a stable foam is produced. It has been found that these constituents are collected by the gas bubbles as they pass upwardly through the oil and are concentrated at the gas-liquid interfaces in the foam above the oil phase. By separating the foam containing the metals from the oil, oil of substantially reduced metals content can be obtained. The invention provides a process for the removal of innate metallic compounds from hydrocarbon oils which is both highly effective and economically attractive.

The process of the invention, which may be referred to as foam fractionation, can be better understood by rst considering the nature and properties of the metallic compounds found in hydrocarbon oils. These compounds are innate constituents of crude oil which upon distillation appear in the heavy fractions boiling above about 950 F. They are nonvolatile at temperatures below about l050 F. and are thus present in distillates having an upper end point between 950 and 1050u F. as a result of entrainment during fractionation. Analyses have shown that the metals are usually complex organic compounds of the porphyrin type in which a central atom of iron, nickel, vanadium or a similar metal is surrounded by four pyrole rings interconnected by 2,897,144 Patented July 28, 1959 methene linkages. Various substituents including alkyl chains, alkylene groups and carboxylic acid radicals may be attached to each of the pyrrole rings and in some cases the individual porphyrin molecules may polymerize to give even more complex structures.

Because of their structure, the metallic constituents found in high boiling hydrocarbon oils exhibit a high degree of surface activity. This provides a means for their separation from the bulk of the oil which is nonsurface active. By providing a large phase interface at which surface-active materials tend to concentrate to the exclusion of non-surface active constituents,a separation can be made between the metallic compounds and the bulk of the oil. Foaming the oil provides the necessary phase interface.

In carrying out the separation described above, gas is introduced into oil, foam is formed and the surfaceactive constituents are concentrated in the oil-gas interfaces surrounding the gas bubbles and are thus carried into the foam phase above the oil. The foam is withdrawn overhead from the foaming vessel and oil of reduced metals content is taken off as a bottoms product. The foam recovered may be collapsed and a part of the oil obtained therefrom may be reuxed to enrich Subsequent foam in metals content and reduce the loss of oil.

The gas employed for the production of foam in accordance with the invention is not critical and any of a number of gases commonly available may be rutilized. These include inert gases such as carbon dioxide and nitrogen; hydrocarbons such as methane, ethane, ethylene, propane, propylene, butane and mixtures of refinery gases; and other gases such as air, ammonia, oxygen and steam. Gases which can be readily condensed, particularly the heavier hydrocarbon gases and superheated steam, are often preferred because they permit collapse of the foam by condensation and facilitate the recovery of any volatile components of the oil which may have been distilled oif during the foaming process.

The hydrocarbon oils which may be treated for the removal of metallic contaminants in accordance with the invention in general are those including constituents boiling in excess of about 950 F. Although the metallic compounds are found only in oils boiling above about 950 F., the presence of lower boiling constituents in the oils treated by the process is not objectionable andin most cases is desirable because of the high viscosities of fractions boiling wholly above 950 F. It has been found that viscosity has a pronounced effect upon the foaming properties of oils and that some very heavyV fractions will not foam satisfactorily. It is therefore preferred to treat broad fractions having initial boiling points well below 950 F. or to dilute the heavy fractions boiling above that temperature with low viscosity hydrocarbon diluents prior to treating. Preferred diluents include aliphatic hydrocarbon solvents boiling between about 200 F. and about 400 F., kerosines, heavy naphthas and the like. Water may also be added to the oils to promote foaming but this is not always satisfactory because of the emulsion problems sometimes encountered.

In carrying out the process of the invention, the gas may be introduced into the oil in a number of diiferent ways. The simplest and preferred method consists of injecting the gas through one or more orifices located beneath the oil surface. A sparge, a perforated plate or the like may be used in order to distribute the gas bubbles and obtain better contact with the oil than can be had when a single orifice is used. Alternate procedures for introducing the gas include the injection of liquefied gases into the oil at controlled rates so that they vaporize l therein and the use of various agitating devices.

The foam produced in carrying out the process of the invention can usually be collapsed by simply passing it from the foaming vessel into a separation vessel. Foam persistence is governed by the surface tension and viscosity ofthe oil, the bubble size and the temperature and a foam which will readily collapse upon reaching the separation vessel can generally'be produced by regulating the solvent-to-oil ratio, the size of the orifices through which the gas is introduced and the operating temperature. Other well known methods of collapsing foams, such as sudden changes in temperature or pressure or electrical fields, may also be used. lf a condensible vapor such as steam is used as the foaming gas, the foam may be collapsed by condensation as mentioned heretofore. This method will, or course, require separation of the condensed vapor from the oil by decanting, ashing or the like before the oil is refluxed to the foaming step of the process.

The exact nature and objects of the invention may be more fully understood by referring to the following detailed description of a preferred embodiment of the process employed and to the accompanying drawing.

Referring now to the drawing, a hydrocarbon oil containing constituents boiling above about 950 F. and including metallic constituents of the porphyrin type is introduced into foaming vessel 1 through line 2. The foaming vessel should be a vertical tower having suicient space therein to permit enrichment of the foam in contaminants content by refluxing action. Feed line 2 terminates within the foaming vessel in a spray head 3 by means of which the feed may be evenly distributed over the cross-section of the vessel. Kerosine or other suitable hydrocarbon solvent is introduced into the foaming vessel through line 4 and spray nozzle 5. Alternatively the solvent may instead be mixed with the oil and introduced concomitant therewith. The latter procedure is generally preferred because it facilitates injection of the oil in a ne spray and thus assures better contact between the oil and the foam in the vessel. Preferred solvent-to-oil ratios range between about 1:1 and about 4:1. The solvent selected should be substantially nonvolatile at the temperature employed in carrying out the process in order to avoid undue solvent losses by evaporation. Air or other gas is introduced at ambient temperature into the bottom of foaming vessel 1 through line 6 and sparge or other distribution device 7 and bubbled upwardly through the oil therein. The oil level in the vessel is indicated by reference numeral S and is maintained at an intermediate point between the levels at which the feed and gas are introduced. Normally it is preferred to carry out the foaming step of the process at ambient temperatures but when using condensible gases such as steam the oil temperature must be maintained sufciently high to prevent condensation within the foaming vessel. Vessel 1 may be provided with coils, jacketing or other heating means in order to maintain the proper temperature therein. Unduly high temperatures should be avoided, since they may interfere with the foaming action. The linear velocity of the gas introduced into the foaming vessel may be varied widely depending upon the diameter of the vessel and the viscosity of the liquid. It has, however, been found that the height of the foam phase increases with gas velocity and then drops again. A high foam phase permits oil in the foam to drain back into the oil pool at the bottom of the foaming vessel and thus results in improved separation. Conditions for maximum foam height can be readily determined experimentally for any system.

As the air introduced through line 6 and sparge 7 bubbles through the pool of oil in vessel 1, metallic porphyrins in the oil are collected at the oil-gas interfaces surrounding the bubbles as a result of their surface activity. The bubbles pass upwardly to the surface of the pool, thus forming a foam in which the porphyrins from the bulk of the oil are concentrated. Product oil having a reducedV contaminants content is withdrawn from the pool in vessel 1 through line 9. Since the product oil is taken off at a level below that at which the gas is introduced, there is normally no air present in the oil. In some cases, however, where a condensible vapor is used it may be desirable to pass the oil from line 9 through a separation vessel wherein small amounts of condensate can be decanted or otherwise separated from the product oil.

The foam produced in Vessel 1 as the air bubbles reach the surface of the oil pool therein continuously moves upward in the vessel and is withdrawn therefrom through overhead line 10 to defoaming zone 11. The foam is collapsed in the defoaming zone and air is vented therefrom through line 12. Oil and metallic compounds carried overhead from vessel 1 in the foam are removed from the defoaming zone through line 13. A portion of this metals-containing oil is withdrawn from the system through line 14 but the major part is transferred through line 15 and spray nozzle 16 into the upper part of vessel 1 as reflux. Reflux ratios may range from 1:1 to as much as 10:1 or higher. The reiiux oil rich in metals passes downwardly through the vessel countercurrent toV the rising foam. Metals present in the reflux are stripped therefrom by the foam and thus the concentration of metals in the foam is increased. The reux oil from which the metals are stripped serves to increase the product oil yield. A distillation step, not shown, may be employed for removing the solvent from the product oil.

The invention may be illustrated still further by considering experiments which were carried out for the removal of metallic porphyrins from a hydrocarbon oil by foam fractionation.

EXAMPLE l In therst of a series of experiments, a crude oil containing a high vanadium concentration was diluted with an aliphatic petroleum solvent boiling between about 300 and 400 F. in a ratio of 1 part of oil to 3 parts of solvent. This solution was then introduced into a glass column and carbon dioxide was hubbled through the solution in the bottom of the column at room temperature. A fritted glass tube was used for the introduction of the gas. The gas rate was continually increased during the course of the run. Foam was produced and taken overhead from the column to a collection vessel where it was collapsed. Three overhead foam fractions were collected during the course of the run. These, together with the feed and the bottoms fraction from the column, were then analyzed for their vanadium contents. The results obtained were as follows:

Overhead fractions Feed First Second Third Bottoms Vanadium content,

p.p.m 150. 3 140.1 116. 2 196. 3 54. 0

Start;

Gas rate, s.c.f.h 0. 4-0. 5 1.6-2.0 2.0-2.5 2. 5-4. 5

EXAMPLE 2 A crude oil similar to that employed in the previous example was diluted with three volumes of a light hydro- A`Carbon solvll boiling between about 300 F. and about 400 F. The solution thus formed was then charged into a foam fractionating column. Carbon dioxide was bubbled into the bottom of the column and foam was formed immediately. The foaming was carried out at a temperature of 91 F. The gas rate was maintained at from 4 to 5 s.c.f.h. The foam produced Was taken overhead from the column into a foam breaking vessel where it readily collapsed. Upon analysis of the product oil withdrawn from the bottom of the foam fractionation column it was found that the metallic porphyrins con tent of the oil had been reduced as follows:

It will be appreciated that a number of modications may be made in the process of the invention as described herein without departing from the scope thereof. The process is not limited to the treatment of high boiling petroleum fractions containing metallic porphyrins and may be employed for the removal of surface active materials from shale oil and other hydrocarbon oils. Foam fractionation is a particularly attractive method for the refining of shale oils because of the high concentration of surface active nitrogen, oxygen and sulfur compounds found in such oils. These, as Well as metallic porphyrins, can readily be removed from such oils by the process of the invention.

What is claimed is:

1. An improved process for removing surface active constituents from a hydrocarbon oil which comprises foaming a portion of said oil with a non-reactive gas and separately recovering foam containing surface active compounds and oil substantially reduced in surface active constituents.

2. An improved process for removing surface active constituents from a hydrocarbon oil which comprises foaming a portion of said oil with a non-reactive gas, separately recovering foam containing surface active compounds and oil substantially reduced in surface active constituents, collapsing said recovered foam and recovering oil containing surface active compounds therefrom, and reuxing a portion of said oil containing surface active compounds in countercurrent contact with foam from said foaming step.

3. A process as defined by claim 2 wherein gas is bubbled through said oil to produce foam.

4. A process as defined by claim 2 wherein said oil is diluted with a solvent prior to said foaming.

5. An improved process for removing metallic porphyrins from a petroleum fraction including constituents boiling in excess of about 950 F. which comprises bubbling a non-reactive gas through said oil and forming a foam in which porphyrins are concentrated, separately withdrawing foam containing porphyrins and oil having a substantially reduced porphyrins content, collapsing said withdrawn foam and recovering oil containing porphyrins, and refluxing a portion of said oil containing porphyrins in countercurrent contact with said foam containing porphyrins,

6. A process as defined by claim 5` wherein said gas is a vapor and said foam is collapsed by condensation of said vapor.

7. A process as defined by claim 5 wherein said oil is diluted with from l to 4 volumes of a 10W viscosity solvent prior to foaming.

8. A process as defined by claim 5 wherein said gas is air.

References Cited in the le of this patent UNITED STATES PATENTS 

1. AN IMPROVED PROCESS FOR REMOVING SURFACE ACTIVE CONSTITUENTS FRO A HYDROCARBON OIL WHICH COMPRISES FOAMING A PORTION OF SIAD OIL WITH A NON-REACTIVE GAS AND SEPARATELY RECOVERING FOAM CONTAINING SURFACE ACTIVE COMPOUNDS AND OIL SUBSTANTIALLY REDUCED IN SURFACE ACTIVE CONSTITUENTS. 